Yanmar Cold Air Intake

[stollo770]

Hello,

I have a Yanmar SB8 diesel engine in a 1979 Hunter 27. With the boat out of the water for the winter I have had time to ponder many things, and one of those things is adding a cold air intake to my Yanmar SB8. The engine runs fine and I think its a good idea, but I just want to run it by you guys in the forum first to make sure I'm not tampering with something that I shouldn't be.

I'm basing my idea off of the fact that all engines need Oxygen to run, and the more they have at their disposal the better they run. The Yanmar SB8 intakes it's air from a piece of stainless steel tubing at the front of the engine. The tubing has no filter, and stops just above the alternator belt inside the engine bay. This means that when the running engine gets hot and the engine bay heats up, the engine is sucking in very hot (and potentially dirty) air. Hot air has less Oxygen content in it per unit and so I am assuming that my diesel engine does not like this (though it puts up with it).

So what I am thinking about doing is bending the intake pipe at a 90 degree angle, away from the alternator belt, and attaching it to a new pipe that extends aft towards the stern clam shell vents. That way when the engine runs it will be using fresh, cooler air and will run better.

Does this sound like a good idea or should I leave well enough alone? Though I am confident with the concepts I feel like if it is such a good idea then Hunter would have done it already (and they didn't). Any advice would be much appreciated.

Thank you,
-Stollo770

 

[RichH]

Leave it alone. Diesel cycle engines depend on HEAT to operate. Less heat = less compression = less ignition efficiency.

 

[kloudie1]

"theoretically" the engine would make more horsepower with colder air.. but on a diesel, this would only happen when the governor has fully advanced the flow control on the pump.. It would be a small enough gain that you'd have to have sophisticated instruments to show it; certainly would not be noticeable in everyday use.. In real life, as Rich notes, the hotter air makes the fuel ignite better and because you aren't heating the air as much with burning fuel, the engine is a little more efficient.. again very small effects.. much less than a dirty prop or bottom.

 

[Terry411]

Cold clean air is the best for your engine. Will you notice a difference probably not, but it won't hurt.
You could also get a side benefit of quieter operation if you use a modern air box.

 

[stollo770]

Thanks everyone for the advice. I'll leave the engine alone. I don't want to upset the balance between heat and efficiency and it sounds like any marginal gains wouldn't be worth the work to get them.

 

[Benny17441]

Yes, do not mess with it, when the engine has reached its operating temperature the air inside the engine compartment is mostly kept at a constant temperature range irrespective of the ambient temperature fluctuations. The diesel engine burns the air fuel mixture by heating it through compression. These engines work more efficiently when hot and the introduction of fluctuating ambient cold air could actually reduce their efficiency and thus performance. Also you are looking at a 1GM, 318cc slow revving 6.5 HP engine and there is not much that can be done to improve its performance in a significant manner. Gasoline engines burn their air fuel mixture with a timed spark and will benefit from a colder and richer intake air but not diesels.

 

[Terry411]

If hot air is what is best, why do truck company engineers spend so much money and time designing cold air intakes?

 

[Benny17441]

If hot air is what is best, why do truck company engineers spend so much money and time designing cold air intakes?[/QUOTE

They did some Dyno testing of trucks with aftermarket filters and intake systems and could not find any increase in horsepower. The amount of air provided by a Turbocharger remained constant. A separate study looked at fuel mileage and although some minute gains were found vs. the base they could not directly attribute the gains exclusively to the intake system. They did indeed find that some of these filters were letting in more particles of contaminants than their stock counterparts while the amount of air that both allowed through remained fairly constant. The after market industry is pushing the sale of these cold air intake systems because the concept sells. Those systems usually dress up the engines and gives them a deeper growling sound which is appealing to some but seem to have no performance gains over the stock systems. Anyways, we cannot compare our auxiliary engines to some of these mammoth 7 liter truck engines. It seems the effort to improve performance of our small engines through modifications to the air intake system is unwarranted.

 

[braol]

I'd at least go with an air filter. I have the same engine and have contemplated at least the filtration question. Something like a cone filter might do the trick.

 

[RichH]

One must be careful with retro-fitting 'economy' retrofits on internal combustion engines. Most IC engines are by design a wee bit 'overfueled' which helps to control the operating temperatures inside the combustion chamber - the unburnt fuel exiting helps to remove heat. Leaning out the combustion mixture lessens the over-fueling which increases combustion temperature ... and can add to internal wear in diesel engines. If you 'lean out' to the max., expect at a worst case, that you can more easily burn a hole through a piston top.

 

[Terry411]

If hot air is what is best, why do truck company engineers spend so much money and time designing cold air intakes?[/QUOTE

They did some Dyno testing of trucks with aftermarket filters and intake systems and could not find any increase in horsepower. The amount of air provided by a Turbocharger remained constant. A separate study looked at fuel mileage and although some minute gains were found vs. the base they could not directly attribute the gains exclusively to the intake system. They did indeed find that some of these filters were letting in more particles of contaminants than their stock counterparts while the amount of air that both allowed through remained fairly constant. The after market industry is pushing the sale of these cold air intake systems because the concept sells. Those systems usually dress up the engines and gives them a deeper growling sound which is appealing to some but seem to have no performance gains over the stock systems. Anyways, we cannot compare our auxiliary engines to some of these mammoth 7 liter truck engines. It seems the effort to improve performance of our small engines through modifications to the air intake system is unwarranted.

I was speaking of OEM truck intakes. Yes hard to beat them now days without increased noise. If the engine area on the op 27 is like the 30's or 37's I had, it gets very hot in there. A little fresh air would help. I have a blower on my boat to pull the hot air out and cooler air in and the engine room is still hot. But like you I and most other said he will most likely not notice a difference in operation of the engine.

 

[seadaddler]

Air Filters

Just to let you know that I tried one of those after market air filter like some one on this forum and it is more for auto racers that I got in the auto parts store and think it was K&N.
The noise in my cockpit was like one of those Hot Rod cars and I thought if my wife was down below like in the galley
she would not be happy and many times when motoring she will make me a drink
or some thing to eat but I changed that thing out and back to the stock metal type filter that is stock.
I have been told by other sailor's that my H-36 is very quiet and they love how it steers and handles and the engine always smooth,:dance::dance::dance::dance:
Just a warning on changing the filter and I have a exhaust blower that helps take heat out.
Nick